Compounds capable of absorbing light in the visible region provide various colors according to the wavelength of the light absorbed. These compounds are also called a dye or a dyestuff and used for coloring various materials. Their use in high-level technology includes a dye for an optical disc which is a high-density information recording material, a spectral sensitizing dye of silver halide photography or electrophotography which are an image information recording material, and a filter dye. Further, in recent years, their medicinal use in phototherapy is attracting attention.
The dyes used as described above are in many cases formed into a solution and then worked to form a desired state. Accordingly, they are required to have excellent solubility. Further, in the case when the dyes are used as a dye for optical disc or as a spectral sensitizing dye, a solid state or an adsorbed state is formed and therefore, different from the solution state, the properties as a molecular aggregate greatly participate in the performance. A slight change of the molecular structure very commonly gives large effects on the solubility or formation of a molecular aggregate.
Methine compounds having a partial structure comprising a heterocyclic ring having several sulfoalkyl groups are known. As the sulfoalkyl group, a 2-sulfoethyl group, a 3-sulfopropyl group, a 4-sulfobutyl group and a 3-sulfobutyl group are well known. With respect to the sulfoalkenyl group, only two groups are known in British Patent 1,077,611. The difference in the structure of the substituent affects the solubility or formation of a molecular aggregate of the above-described dyes. Accordingly, to develop new sulfoalkenyl groups may achieve more variation of the properties of the methine compound and is very expected.
On the other hand, an enormous number of efforts have been conventionally made to achieve high sensitivity of silver halide photographic light-sensitive materials. The sensitizing dye used for the spectral sensitization is known to have large effects on the capability of the silver halide photographic light-sensitive material. A slight difference in the structure of the sensitizing dye greatly affects the photographic capabilities such as sensitivity, fog and storage stability, however, to foresee the effects in advance is difficult and many research workers have hitherto synthesized a large number of sensitizing dyes and very intensely examined the photographic capabilities of the dyes. As the sensitizing dye, those having a partial structure comprising a nitrogen-containing heterocyclic ring having a sulfoalkyl group are very often used. The sulfoalkyl group well known includes a 2-sulfoethyl group, a 3-sulfopropyl group, a 4-sulfobutyl group and a 3-sulfobutyl group. With respect to the sulfoalkenyl group, only two groups are known in British Patent 1,077,611. However, sulfoalkenyl groups other than these have not yet been investigated and accordingly, their photographic capabilities cannot be anticipated at all at present.
The quaternary salt compound as a starting material of the methine compound of the present invention has hitherto been thoroughly not known and its photographic capabilities cannot be anticipated at all at present.